An International Multicenter Replication Framework for Concentration-Independent Qualitative Fibrinogen Phenotypes: Clinical Harmonization, Prespecified Estimands, and Independent Validation

An International Multicenter Replication Framework for Concentration-Independent Qualitative Fibrinogen Phenotypes: Clinical Harmonization, Prespecified Estimands, and Independent Validation This methodological article proposes an international multicenter framework for the independent clinical replication of concentration-independent qualitative fibrinogen phenotypes. It builds upon previously proposed experimental protocols and laboratory qualification procedures, extending the research program from analytical reproducibility toward clinically interpretable, independently testable biological associations. The central objective is to determine whether functional differences between characterized fibrinogen preparations persist after concentration matching and can be reproduced across independent clinical populations, laboratories, and analytical settings. Stable, non-dialysis chronic kidney disease (CKD), particularly stages G3b–G4, is presented as a conditional initial clinical model because of its biological plausibility for investigating molecular alterations such as fibrinogen carbamylation. This selection remains a methodological proposal rather than an established demonstration of disease-specific fibrinogen dysfunction. The framework integrates harmonized clinical eligibility criteria, standardized biospecimen collection and processing, fibrinogen purification quality control, blinded functional measurements, prespecified statistical estimands, and explicit procedures for evaluating center-level heterogeneity, confounding, missing data, and analytical batch effects. A candidate primary functional endpoint is direct-plasmin clot-lysis half-time (t50), measured under controlled experimental conditions using characterized fibrinogen preparations at matched concentrations. The proposed primary analysis evaluates differences on the logarithmic scale, with results interpretable as adjusted geometric mean ratios when model assumptions are satisfied. Particular emphasis is placed on distinguishing four levels of evidence: Analytical reproducibility of the functional assay. Replication of a concentration-independent clinical association. Causal attribution to specific fibrinogen molecular modifications. Demonstration of physiological or clinical consequences. The manuscript incorporates four methodological tables, a multicenter study workflow, statistical considerations, independent replication requirements, and prespecified GO/MODIFY/HOLD/NO-GO criteria. The framework is designed to accommodate negative, heterogeneous, or inconclusive findings without treating them as failures of the broader research program. A reproducible clinical association would not, by itself, establish molecular causality, microvascular dysfunction, or therapeutic relevance. This publication presents a proposed clinical research framework. No completed international multicenter study, validated clinical biomarker, or original clinical outcome dataset is reported. The proposed approach aims to facilitate transparent, collaborative, statistically rigorous, and falsifiable investigation of qualitative fibrinogen phenotypes across independent research centers. Funding: No funding or financial support was received. Competing interests: The author declares no competing interests or conflicts of interests. Zenodo keywords: Fibrinogen; Qualitative Fibrinogen Phenotype; Multicenter Replication; Chronic Kidney Disease; Carbamylation; Fibrinolysis; Concentration-Independent Function; Clinical Research Protocol; Statistical Estimands; Independent Validation; Open Science.